Trailer sensor module and associated method of wireless trailer identification and motion estimation

ABSTRACT

A method of identifying a trailer with a vehicle includes a step of transmitting a unique identifier with a wireless transmitter attached to the trailer. The wireless transmitter may be housed as part of a sensor module with a sensor that senses a parameter of the trailer for operating a trailer backup assist system. The housing of the sensor module may be adapted to be removably attached to the trailer. The unique identifier emitted by the wireless transmitter is received with a wireless receiver on the vehicle. After the unique identifier is recognized by a controller on the vehicle, a parameter of the trailer may be accessed for autonomously guiding the trailer along a desired backing path.

CROSS REFERENCE TO RELATED APPLICATION

This patent application is a continuation-in-part of co-pending U.S.patent application Ser. No. 14/512,859, which was filed on Oct. 13,2014, entitled “TRAILER MOTION AND PARAMETER ESTIMATION SYSTEM,” whichhas a common Applicant herewith and the entire contents of which ishereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The disclosure made herein relates generally to trailer identificationand motion estimation, and more particularly to a trailer sensor modulein communication with a towing vehicle for wireless traileridentification and hitch angle estimation to assist with autonomousvehicle guidance of the trailer, such as a trailer backup assist system.

BACKGROUND OF THE INVENTION

Reversing a vehicle while towing a trailer can be challenging for manydrivers, particularly for drivers that drive with a trailer on aninfrequent basis or with various types of trailers. Systems used toassist a driver with backing a trailer frequently estimate the positionof the trailer relative to the vehicle with a sensor that determines ahitch angle. The accuracy and reliability of this hitch angle estimationcan be critical to the operation of the backup assist system. It is alsounderstood that reliable hitch angle estimation can be useful foradditional vehicle features, such as monitoring for trailer sway.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a method ofidentifying a trailer with a vehicle includes transmitting a uniqueidentifier with a wireless transmitter attached to the trailer. Themethod also includes receiving the unique identifier with a wirelessreceiver on the vehicle. Further, the method includes accessing aparameter of the trailer based on the received unique identifier forautonomously guiding the trailer along a desired backing path.

According to another aspect of the present invention, a trailer sensormodule for communicating with a vehicle includes a sensor that senses aparameter of the trailer for operating a trailer backup assist system.The trailer sensor module also includes a wireless transmitter thatemits a unique identifier configured to be recognized by the vehicleand, upon recognition, transmits the parameter to the vehicle. A housingencloses the wireless transmitter and the sensor, whereby the housing isadapted to be removably attached to the trailer.

According to yet another aspect of the present invention, a trailerbackup assist system for a vehicle reversing a trailer includes awireless transmitter removably coupled with the trailer. The wirelesstransmitter emits a unique identifier. A wireless receiver is coupledwith the vehicle for receiving the unique identifier. Also, a controlleron the vehicle identifies the trailer based on the unique identifier andaccesses a parameter of the identified trailer for autonomously guidingthe trailer with the vehicle along a desired backing path.

These and other aspects, objects, and features of the present inventionwill be understood and appreciated by those skilled in the art uponstudying the following specification, claims, and appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a top perspective view of a vehicle attached to a trailer withone embodiment of a sensor module for operating a trailer backup assistsystem;

FIG. 2 is a block diagram illustrating one embodiment of the trailerbackup assist system having a steering input device, a curvaturecontroller, and a trailer braking system;

FIG. 3 is a schematic diagram that illustrates the geometry of a vehicleand a trailer overlaid with a two-dimensional x-y coordinate system,identifying variables used to determine a kinematic relationship of thevehicle and the trailer for the trailer backup assist system, accordingto one embodiment;

FIG. 4 is a schematic block diagram illustrating portions of a curvaturecontroller, according to an additional embodiment, and other componentsof the trailer backup assist system, according to such an embodiment;

FIG. 5 is schematic block diagram of the curvature controller of FIG. 4,showing the feedback architecture and signal flow of the curvaturecontroller, according to such an embodiment;

FIG. 6 is a schematic diagram showing a relationship between a hitchangle and a steering angle of the vehicle as it relates to curvature ofthe trailer and a jackknife angle;

FIG. 7 is a plan view of a steering input device having a rotatable knobfor operating the trailer backup assist system, according to oneembodiment;

FIG. 8 is a plan view of another embodiment of a rotatable knob forselecting a desired curvature of a trailer and a corresponding schematicdiagram illustrating a vehicle and a trailer with various trailercurvature paths correlating with desired curvatures that may beselected;

FIG. 9 is a schematic diagram showing a backup sequence of a vehicle anda trailer implementing various curvature selections with the trailerbackup assist system, according to one embodiment;

FIG. 10 is a flow diagram illustrating a method of operating a trailerbackup assist system using an operating routine for steering a vehiclereversing a trailer with normalized control of the desired curvature,according to one embodiment;

FIG. 11 is a top perspective view of a trailer sensor module attached toa trailer for communicating with a vehicle, according to one embodiment;

FIG. 12 is a side elevational view of the trailer sensor module shown inFIG. 11;

FIG. 13 is a block diagram illustrating one embodiment of the trailersensor module communicating with one embodiment of the trailer backupassist system;

FIG. 14 is a flow diagram illustrating a method of identifying a trailerand accessing a parameter of the trailer based on a unique identifier,according to one embodiment; and

FIG. 15 is a flow diagram illustrating a method of estimating a hitchangle using a hitch angle estimation routine, according to oneembodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

For purposes of description herein, it is to be understood that thedisclosed trailer backup assist system and the related methods mayassume various alternative embodiments and orientations, except whereexpressly specified to the contrary. It is also to be understood thatthe specific devices and processes illustrated in the attached drawings,and described in the following specification are simply exemplaryembodiments of the inventive concepts defined in the appended claims.While various aspects of the trailer backup assist system and therelated methods are described with reference to a particularillustrative embodiment, the disclosed invention is not limited to suchembodiments, and additional modifications, applications, and embodimentsmay be implemented without departing from the disclosed invention.Hence, specific dimensions and other physical characteristics relatingto the embodiments disclosed herein are not to be considered aslimiting, unless the claims expressly state otherwise.

Referring to FIGS. 1-15, reference numeral 10 generally designates atrailer backup assist system for controlling a backing path of a trailer12 attached to a vehicle 14 by allowing a driver of the vehicle 14 tospecify a desired curvature 26 of the backing path of the trailer 12. Inone embodiment, the trailer backup assist system 10 automatically steersthe vehicle 14 to guide the trailer 12 on the desired curvature orbacking path 26 as a driver uses the accelerator and brake pedals tocontrol the reversing speed of the vehicle 14. The trailer backup assistsystem 10 may more precisely guide the trailer 12 on the desiredcurvature or backing path 26 with an accurate understanding of theparameters of the trailer 12, which may include the trailer dynamicvariables, such as yaw rate and/or acceleration, and trailer dimensions,such as trailer length. In one embodiment, a trailer sensor module 20may be attached to the trailer 12 and provided with a wirelesstransmitter 29 for transmitting a unique identifier associated with thetrailer 12. Accordingly, in such an embodiment, the vehicle 14 mayinclude a wireless receiver 31 that receives the unique identifier and acorresponding controller that accesses a parameter of the trailer 12based on recognition of the received unique identifier. It iscontemplated that the trailer sensor module 20 may be used inassociation with additional or alternative vehicle features for thetrailer backup assist system 10, such as a trailer sway avoidancesystem.

To monitor the position of the trailer 12 relative to the vehicle 14,the trailer backup assist system 10 may include a sensor system 16 thatsenses or otherwise determines a hitch angle γ between the trailer 12and the vehicle 14. In one embodiment, the sensor system 16 may includethe sensor module 20 attached to the trailer 12 that monitors thedynamics of the trailer 12, such as yaw rate, and communicates with acontroller 28 of the trailer backup assist system 10 to determine theinstantaneous hitch angle γ. Accordingly, one embodiment of a sensormodule 20 is adapted to attach to the trailer 12 and generate a traileryaw rate ω₂. Upon recognition of the attached trailer 12, the wirelesstransmitter 29 may then transmit the trailer yaw rate ω₂ to the vehicle14. The trailer backup assist system 10 according to such an embodimentmay also include a vehicle sensor system 17 that generates a vehicle yawrate ω₁ and a vehicle speed v₁. The controller 28 of the trailer backupassist system 10 may thereby estimate a hitch angle γ based on thetrailer yaw rate ω₂, the vehicle yaw rate ω₁, and the vehicle speed v₁in view of a kinematic relationship between the trailer 12 and thevehicle 14. In another embodiment, the sensor system 16 may, separatefrom the sensor module 20, include a hitch angle sensor 44, such as avision-based system that employs a camera 46 on the vehicle 14 tomonitor a target 52 on the trailer 12 to determine the hitch angle γ andthereby increase accuracy and reliability of the estimated hitch angleγ.

With respect to the general operation of the trailer backup assistsystem 10, a steering input device 18 may be provided, such as arotatable knob 30, for a driver to provide the desired curvature 26 ofthe trailer 12. As such, the steering input device 18 may be operablebetween a plurality of selections, such as successive rotated positionsof a knob 30, that each provide an incremental change to the desiredcurvature 26 of the trailer 12. Upon inputting the desired curvature 26,the controller may generate a steering command for the vehicle 14 toguide the trailer 12 on the desired curvature 26 based on the estimatedhitch angle γ and a kinematic relationship between the trailer 12 andthe vehicle 14. Therefore, the accuracy of the hitch angle estimation iscritical to operating the trailer backup assist system 10. However, itis appreciated that such a system for instantaneously estimating hitchangle may be used in association with additional or alternative vehiclefeatures, such as trailer sway monitoring.

With reference to the embodiment shown in FIG. 1, the vehicle 14 is apickup truck embodiment that is equipped with one embodiment of thetrailer backup assist system 10 for controlling the backing path of thetrailer 12 that is attached to the vehicle 14. Specifically, the vehicle14 is pivotally attached to one embodiment of the trailer 12 that has abox frame 32 with an enclosed cargo area 34, a single axle having aright wheel assembly and a left wheel assembly, and a tongue 36longitudinally extending forward from the enclosed cargo area 34. Theillustrated trailer 12 also has a trailer hitch connector in the form ofa coupler assembly 38 that is connected to a vehicle hitch connector inthe form of a hitch ball 40. The coupler assembly 38 latches onto thehitch ball 40 to provide a pivoting ball joint connection 42 that allowsfor articulation of the hitch angle γ. It should be appreciated thatadditional embodiments of the trailer 12 may alternatively couple withthe vehicle 14 to provide a pivoting connection, such as by connectingwith a fifth wheel connector. It is also contemplated that additionalembodiments of the trailer may include more than one axle and may havevarious shapes and sizes configured for different loads and items, suchas a boat trailer or a flatbed trailer.

Still referring to FIG. 1, the sensor system 16 in the illustratedembodiment includes both a sensor module 20 and a vision-based hitchangle sensor 44 for estimating the hitch angle γ between the vehicle 14and the trailer 12. The illustrated hitch angle sensor 44 employs acamera 46 (e.g. video imaging camera) that may be located proximate anupper region of the vehicle tailgate 48 at the rear of the vehicle 14,as shown, such that the camera 46 may be elevated relative to the tongue36 of the trailer 12. The illustrated camera 46 has an imaging field ofview 50 located and oriented to capture one or more images of thetrailer 12, including a region containing one or more desired targetplacement zones for at least one target 52 to be secured. Although it iscontemplated that the camera 46 may capture images of the trailer 12without a target 52 to determine the hitch angle γ, in the illustratedembodiment, the trailer backup assist system 10 includes a target 52placed on the trailer 12 to allow the trailer backup assist system 10 toutilize information acquired via image acquisition and processing of thetarget 52. For instance, the illustrated camera 46 may include a videoimaging camera that repeatedly captures successive images of the trailer12 that may be processed to identify the target 52 and its location onthe trailer 12 for determining movement of the target 52 and the trailer12 relative to the vehicle 14 and the corresponding hitch angle γ. Itshould also be appreciated that the camera 46 may include one or morevideo imaging cameras and may be located at other locations on thevehicle 14 to acquire images of the trailer 12 and the desired targetplacement zone, such as on a passenger cab 54 of the vehicle 14 tocapture images of a gooseneck trailer. Furthermore, it is contemplatedthat additional embodiments of the hitch angle sensor 44 and the sensorsystem 16 for providing the hitch angle γ may include one or acombination of a potentiometer, a magnetic-based sensor, an opticalsensor, a proximity sensor, an ultrasonic sensor, a rotational sensor, acapacitive sensor, an inductive sensor, or a mechanical based sensor,such as a mechanical sensor assembly mounted to the pivoting ball jointconnection 42, energy transducers of a reverse aid system, a blind spotsystem, and/or a cross traffic alert system, and other conceivablesensors or indicators of the hitch angle γ to supplement or be used inplace of the vision-based hitch angle sensor 44.

The embodiment of the sensor module 20 illustrated in FIG. 1 includes ahousing 21 mounted on the tongue 36 of the trailer 12 proximate theenclosed cargo area 34 and includes left and right wheel speed sensors23 on laterally opposing wheels of the trailer 12. The sensor module 20may generate a plurality of signals indicative of various dynamics ofthe trailer 12. The signals may include a yaw rate signal, a lateralacceleration signal, and wheel speed signals generated respectively by ayaw rate sensor 25, an accelerometer 27, and the wheel speed sensors 23.Accordingly, in the illustrated embodiment, the yaw rate sensor 25 andthe accelerometer 27 are contained within the housing 21, although otherconfigurations are conceivable as described in greater detail herein. Itis contemplated that these sensor signals could be compensated andfiltered to remove offsets or drifts, and smooth out noise. Further, thecontroller 28 may utilize processed signals received outside of thesensor system 16, including standard signals from the brake controlsystem 72 and the power assist steering system 62, such as vehicle yawrate ω₁, vehicle speed v₁, and steering angle δ, to estimate the trailerhitch angle γ, trailer speed and related trailer parameters. Asdescribed in more detail below, the controller 28 may estimates thehitch angle γ based on the trailer yaw rate ω₂, the vehicle yaw rate ω₁,and the vehicle speed v₁ in view of a kinematic relationship between thetrailer 12 and the vehicle 14. The controller 28 of the trailer backupassist system 10 may utilize the estimated trailer variables and trailerparameters to control the steering system 62, brake control system 72,and the powertrain control system 74 to assist backing up thevehicle-trailer combination.

With reference to the embodiment of the trailer backup assist system 10shown in FIG. 2, the hitch angle sensor 44 is provided in dashed linesto illustrate that in some embodiments it may be omitted, such as whenthe trailer sensor module 20 is provided with a means to estimate thehitch angle γ. The illustrated embodiment of the trailer backup assistsystem 10 receives vehicle and trailer status-related information fromadditional sensors and devices. This information includes positioninginformation from a positioning device 56, which may include a globalpositioning system (GPS) on the vehicle 14 or a handled device, todetermine a coordinate location of the vehicle 14 and the trailer 12based on the location of the positioning device 56 with respect to thetrailer 12 and/or the vehicle 14 and based on the estimated hitch angleγ. The positioning device 56 may additionally or alternatively include adead reckoning system for determining the coordinate location of thevehicle 14 and the trailer 12 within a localized coordinate system basedat least on vehicle speed, steering angle, and hitch angle γ. Othervehicle information received by the trailer backup assist system 10 mayinclude a speed of the vehicle 14 from a speed sensor 58 and a yaw rateof the vehicle 14 from a yaw rate sensor 60. It is contemplated that inadditional embodiments, the hitch angle sensor 44 and other vehiclesensors and devices may provide sensor signals or other information,such as proximity sensor signals or successive images of the trailer 12,that the controller of the trailer backup assist system 10 may processwith various routines to determine an indicator of the hitch angle γ,such as a range of hitch angles.

As further shown in FIG. 2, one embodiment of the trailer backup assistsystem 10 is in communication with a power assist steering system 62 ofthe vehicle 14 to operate the steered wheels 64 (FIG. 1) of the vehicle14 for moving the vehicle 14 in such a manner that the trailer 12 reactsin accordance with the desired curvature 26 of the trailer 12. In theillustrated embodiment, the power assist steering system 62 is anelectric power-assisted steering (EPAS) system that includes an electricsteering motor 66 for turning the steered wheels 64 to a steering anglebased on a steering command, whereby the steering angle may be sensed bya steering angle sensor 67 of the power assist steering system 62. Thesteering command may be provided by the trailer backup assist system 10for autonomously steering during a backup maneuver and may alternativelybe provided manually via a rotational position (e.g., steering wheelangle) of a steering wheel 68 (FIG. 1). However, in the illustratedembodiment, the steering wheel 68 of the vehicle 14 is mechanicallycoupled with the steered wheels 64 of the vehicle 14, such that thesteering wheel 68 moves in concert with steered wheels 64, preventingmanual intervention with the steering wheel 68 during autonomoussteering. More specifically, a torque sensor 70 is provided on the powerassist steering system 62 that senses torque on the steering wheel 68that is not expected from autonomous control of the steering wheel 68and therefore indicative of manual intervention, whereby the trailerbackup assist system 10 may alert the driver to discontinue manualintervention with the steering wheel 68 and/or discontinue autonomoussteering.

In alternative embodiments, some vehicles have a power assist steeringsystem 62 that allows a steering wheel 68 to be partially decoupled frommovement of the steered wheels 64 of such a vehicle. Accordingly, thesteering wheel 68 can be rotated independent of the manner in which thepower assist steering system 62 of the vehicle controls the steeredwheels 64 (e.g., autonomous steering as commanded by the trailer backupassist system 10). As such, in these types of vehicles where thesteering wheel 68 can be selectively decoupled from the steered wheels64 to allow independent operation thereof, the steering wheel 68 may beused as a steering input device 18 for the trailer backup assist system10, as disclosed in greater detail herein.

Referring again to the embodiment illustrated in FIG. 2, the powerassist steering system 62 provides the controller 28 of the trailerbackup assist system 10 with information relating to a rotationalposition of steered wheels 64 of the vehicle 14, including a steeringangle. The controller 28 in the illustrated embodiment processes thecurrent steering angle, in addition to other vehicle 14 and trailer 12conditions to guide the trailer 12 along the desired curvature 26. It isconceivable that the trailer backup assist system 10, in additionalembodiments, may be an integrated component of the power assist steeringsystem 62. For example, the power assist steering system 62 may includea trailer backup assist algorithm for generating vehicle steeringinformation and commands as a function of all or a portion ofinformation received from the steering input device 18, the hitch anglesensor 44, the power assist steering system 62, a vehicle brake controlsystem 72, a powertrain control system 74, and other vehicle sensors anddevices.

As also illustrated in FIG. 2, the vehicle brake control system 72 mayalso communicate with the controller 28 to provide the trailer backupassist system 10 with braking information, such as vehicle wheel speed,and to receive braking commands from the controller 28. For instance,vehicle speed information can be determined from individual wheel speedsas monitored by the brake control system 72. Vehicle speed may also bedetermined from the powertrain control system 74, the speed sensor 58,and the positioning device 56, among other conceivable means. In someembodiments, individual wheel speeds can also be used to determine avehicle yaw rate, which can be provided to the trailer backup assistsystem 10 in the alternative or in addition to the vehicle yaw ratesensor 60. In certain embodiments, the trailer backup assist system 10can provide vehicle braking information to the brake control system 72for allowing the trailer backup assist system 10 to control braking ofthe vehicle 14 during backing of the trailer 12. For example, thetrailer backup assist system 10 in some embodiments may regulate speedof the vehicle 14 during backing of the trailer 12, which can reduce thepotential for unacceptable trailer backup conditions. Examples ofunacceptable trailer backup conditions include, but are not limited to,a vehicle 14 over speed condition, a high hitch angle rate, trailerangle dynamic instability, a calculated theoretical trailer jackknifecondition (defined by a maximum vehicle steering angle, drawbar length,tow vehicle wheelbase, and an effective trailer length), or physicalcontact jackknife limitation (defined by an angular displacement limitrelative to the vehicle 14 and the trailer 12), and the like. It isdisclosed herein that the trailer backup assist system 10 can issue analert signal corresponding to a notification of an actual, impending,and/or anticipated unacceptable trailer backup condition.

The powertrain control system 74, as shown in the embodiment illustratedin FIG. 2, may also interact with the trailer backup assist system 10for regulating speed and acceleration of the vehicle 14 during backingof the trailer 12. As mentioned above, regulation of the speed of thevehicle 14 may be necessary to limit the potential for unacceptabletrailer backup conditions such as, for example, jackknifing and trailerangle dynamic instability. Similar to high-speed considerations as theyrelate to unacceptable trailer backup conditions, high acceleration andhigh dynamic driver curvature requests can also lead to suchunacceptable trailer backup conditions.

With continued reference to FIG. 2, the trailer backup assist system 10in the illustrated embodiment may communicate with one or more devices,including a vehicle alert system 76, which may prompt visual, auditory,and tactile warnings. For instance, vehicle brake lights 78 and vehicleemergency flashers may provide a visual alert and a vehicle horn 79and/or speaker 81 may provide an audible alert. Additionally, thetrailer backup assist system 10 and/or vehicle alert system 76 maycommunicate with a human machine interface (HMI) 80 for the vehicle 14.The HMI 80 may include a vehicle display 82, such as a center-stackmounted navigation or entertainment display (FIG. 1). Further, thetrailer backup assist system 10 may communicate via wirelesscommunication with another embodiment of the HMI 80, such as with one ormore handheld or portable devices, including one or more smartphones.The portable device may also include the display 82 for displaying oneor more images and other information to a user. For instance, theportable device may display one or more images of the trailer 12 and anindication of the estimated hitch angle on the display 82. In addition,the portable device may provide feedback information, such as visual,audible, and tactile alerts.

As further illustrated in FIG. 2, the trailer backup assist system 10includes a steering input device 18 that is connected to the controller28 for allowing communication of information therebetween. It isdisclosed herein that the steering input device 18 can be coupled to thecontroller 28 in a wired or wireless manner. The steering input device18 provides the trailer backup assist system 10 with informationdefining the desired backing path of travel of the trailer 12 for thecontroller 28 to process and generate steering commands. Morespecifically, the steering input device 18 may provide a selection orpositional information that correlates with a desired curvature 26 ofthe desired backing path of travel of the trailer 12. Also, the trailersteering commands provided by the steering input device 18 can includeinformation relating to a commanded change in the path of travel, suchas an incremental change in the desired curvature 26, and informationrelating to an indication that the trailer 12 is to travel along a pathdefined by a longitudinal centerline axis of the trailer 12, such as adesired curvature value of zero that defines a substantially straightpath of travel for the trailer. As will be discussed below in moredetail, the steering input device 18 according to one embodiment mayinclude a movable control input device for allowing a driver of thevehicle 14 to command desired trailer steering actions or otherwiseselect and alter a desired curvature. For instance, the moveable controlinput device may be a rotatable knob 30, which can be rotatable about arotational axis extending through a top surface or face of the knob 30.In other embodiments, the rotatable knob 30 may be rotatable about arotational axis extending substantially parallel to a top surface orface of the rotatable knob 30. Furthermore, the steering input device18, according to additional embodiments, may include alternative devicesfor providing a desired curvature 26 or other information defining adesired backing path, such as a joystick, a keypad, a series ofdepressible buttons or switches, a sliding input device, various userinterfaces on a touch-screen display, a vision based system forreceiving gestures, a control interface on a portable device, and otherconceivable input devices as generally understood by one having ordinaryskill in the art. It is contemplated that the steering input device 18may also function as an input device for other features, such asproviding inputs for other vehicle features or systems.

Still referring to the embodiment shown in FIG. 2, the controller 28 isconfigured with a microprocessor 84 to process logic and routines storedin memory 86 that receive information from the sensor system 16,including the trailer sensor module 20, the hitch angle sensor 44, thesteering input device 18, the power assist steering system 62, thevehicle brake control system 72, the trailer braking system, thepowertrain control system 74, and other vehicle sensors and devices. Thecontroller 28 may generate vehicle steering information and commands asa function of all or a portion of the information received. Thereafter,the vehicle steering information and commands may be provided to thepower assist steering system 62 for affecting steering of the vehicle 14to achieve a commanded path of travel for the trailer 12. The controller28 may include the microprocessor 84 and/or other analog and/or digitalcircuitry for processing one or more routines. Also, the controller 28may include the memory 86 for storing one or more routines, including ahitch angle estimation routine 130, an operating routine 132, and acurvature routine 98. It should be appreciated that the controller 28may be a stand-alone dedicated controller or may be a shared controllerintegrated with other control functions, such as integrated with thesensor system 16, the power assist steering system 62, and otherconceivable onboard or off-board vehicle control systems.

With reference to FIG. 3, we now turn to a discussion of vehicle andtrailer information and parameters used to calculate a kinematicrelationship between a curvature of a path of travel of the trailer 12and the steering angle of the vehicle 14 towing the trailer 12, whichcan be desirable for a trailer backup assist system 10 configured inaccordance with some embodiments, including for use by a curvatureroutine 98 of the controller 28 in one embodiment. To achieve such akinematic relationship, certain assumptions may be made with regard toparameters associated with the vehicle/trailer system. Examples of suchassumptions include, but are not limited to, the trailer 12 being backedby the vehicle 14 at a relatively low speed, wheels of the vehicle 14and the trailer 12 having negligible (e.g., no) slip, tires of thevehicle 14 having negligible (e.g., no) lateral compliance, tires of thevehicle 14 and the trailer 12 having negligible (e.g., no) deformation,actuator dynamics of the vehicle 14 being negligible, and the vehicle 14and the trailer 12 exhibiting negligible (e.g., no) roll or pitchmotions, among other conceivable factors with the potential to have aneffect on controlling the trailer 12 with the vehicle 14.

As shown in FIG. 3, for a system defined by a vehicle 14 and a trailer12, the kinematic relationship is based on various parameters associatedwith the vehicle 14 and the trailer 12. These parameters include:

δ: steering angle at steered front wheels of the vehicle;

α: yaw angle of the vehicle;

β: yaw angle of the trailer;

γ: hitch angle (γ=β−α);

W: wheel base of the vehicle;

L: length between hitch point and rear axle of the vehicle;

D: distance between hitch point and axle of the trailer or effectiveaxle for a multiple axle trailer (axle length may be an equivalent); and

r₂: curvature radius for the trailer.

One embodiment of a kinematic relationship between trailer path radiusof curvature r₂ at the midpoint of an axle of the trailer 12, steeringangle δ of the steered wheels 64 of the vehicle 14, and the hitch angleγ can be expressed in the equation provided below. As such, if the hitchangle γ is provided, the trailer path curvature κ₂ can be controlledbased on regulating the steering angle δ (where {dot over (β)} istrailer yaw rate and {dot over (η)} is trailer velocity).

$\kappa_{2} = {\frac{1}{r_{2}} = {\frac{\overset{.}{\beta}}{\overset{.}{\eta}} = \frac{{\left( {W + \frac{{KV}^{2}}{g}} \right)\sin \; \gamma} + {L\; \cos \; \gamma \; \tan \; \delta}}{D\left( {{\left( {W + \frac{{KV}^{2}}{g}} \right)\cos \; \gamma} - {L\; \sin \; \gamma \; \tan \; \delta}} \right)}}}$

This relationship can be expressed to provide the steering angle δ as afunction of trailer path curvature κ₂ and hitch angle γ.

$\delta = {{\tan^{- 1}\left( \frac{\left( {W + \frac{{KV}^{2}}{g}} \right)\left\lbrack {{\kappa_{2}D\; \cos \; \gamma} - {\sin \; \gamma}} \right\rbrack}{{{DL}\; \kappa_{2}\sin \; \gamma} + {L\; \cos \; \gamma}} \right)} = {F\left( {\gamma,\kappa_{2},K} \right)}}$

Accordingly, for a particular vehicle and trailer combination, certainparameters (e.g., D, W and L) of the kinematic relationship are constantand assumed known. V is the vehicle longitudinal speed and g is theacceleration due to gravity. K is a speed dependent parameter which whenset to zero makes the calculation of steering angle independent ofvehicle speed. For example, vehicle-specific parameters of the kinematicrelationship can be predefined in an electronic control system of thevehicle 14 and trailer-specific parameters of the kinematic relationshipcan be inputted by a driver of the vehicle 14, determined from sensedtrailer behavior in response to vehicle steering commands, or otherwisedetermined from signals provided by the trailer 12. Trailer pathcurvature κ₂ can be determined from the driver input via the steeringinput device 18. Through the use of the equation for providing steeringangle, a corresponding steering command can be generated by thecurvature routine 98 for controlling the power assist steering system 62of the vehicle 14.

In an additional embodiment, an assumption may be made by the curvatureroutine 98 that a longitudinal distance L between the pivotingconnection and the rear axle of the vehicle 14 is equal to zero forpurposes of operating the trailer backup assist system 10 when agooseneck trailer or other similar trailer is connected with the a hitchball or a fifth wheel connector located over a rear axle of the vehicle14. The assumption essentially assumes that the pivoting connection withthe trailer 12 is substantially vertically aligned with the rear axle ofthe vehicle 14. When such an assumption is made, the controller 28 maygenerate the steering angle command for the vehicle 14 as a functionindependent of the longitudinal distance L between the pivotingconnection and the rear axle of the vehicle 14. It is appreciated thatthe gooseneck trailer mentioned generally refers to the tongueconfiguration being elevated to attach with the vehicle 14 at anelevated location over the rear axle, such as within a bed of a truck,whereby embodiments of the gooseneck trailer may include flatbed cargoareas, enclosed cargo areas, campers, cattle trailers, horse trailers,lowboy trailers, and other conceivable trailers with such a tongueconfiguration.

Yet another embodiment of the curvature routine 98 of the trailer backupassist system 10 is illustrated in FIG. 4, showing the generalarchitectural layout whereby a measurement module 88, a hitch angleregulator 90, and a curvature regulator 92 are routines that may bestored in the memory 86 of the controller 28. In the illustrated layout,the steering input device 18 provides a desired curvature κ₂ value tothe curvature regulator 92 of the controller 28, which may be determinedfrom the desired backing path 26 that is input with the steering inputdevice 18. The curvature regulator 92 computes a desired hitch angleγ(d) based on the current desired curvature κ₂ along with the steeringangle δ provided by a measurement module 88 in this embodiment of thecontroller 28. The measurement module 88 may be a memory device separatefrom or integrated with the controller 28 that stores data from sensorsof the trailer backup assist system 10, such as the hitch angle sensor44, the vehicle speed sensor 58, the steering angle sensor, oralternatively the measurement module 88 may otherwise directly transmitdata from the sensors without functioning as a memory device. Once thedesired hitch angle γ(d) is computed by the curvature regulator 92 thehitch angle regulator 90 generates a steering angle command based on thecomputed desired hitch angle γ(d) as well as a measured or otherwiseestimated hitch angle γ(m) and a current velocity of the vehicle 14. Thesteering angle command is supplied to the power assist steering system62 of the vehicle 14, which is then fed back to the measurement module88 to reassess the impacts of other vehicle characteristics impactedfrom the implementation of the steering angle command or other changesto the system. Accordingly, the curvature regulator 92 and the hitchangle regulator 90 continually process information from the measurementmodule 88 to provide accurate steering angle commands that place thetrailer 12 on the desired curvature κ₂ and the desired backing path 26,without substantial overshoot or continuous oscillation of the path oftravel about the desired curvature κ₂.

As also shown in FIG. 5, the embodiment of the curvature routine 98shown in FIG. 4 is illustrated in a control system block diagram.Specifically, entering the control system is an input, K₂, whichrepresents the desired curvature 26 of the trailer 12 that is providedto the curvature regulator 92. The curvature regulator 92 can beexpressed as a static map, p(K₂, (5), which in one embodiment is thefollowing equation:

${p\left( {\kappa_{2},\delta} \right)} = {\tan^{- 1}\left( \frac{{\kappa_{2}{DW}} + {L\; {\tan (\delta)}}}{{\kappa_{2}{DL}\; {\tan (\delta)}} - W} \right)}$

Where,

κ₂ represents the desired curvature of the trailer 12 or 1/r₂ as shownin FIG. 3;

δ represents the steering angle;

L represents the distance from the rear axle of the vehicle 14 to thehitch pivot point;

D represents the distance from the hitch pivot point to the axle of thetrailer 12; and

W represents the distance from the rear axle to the front axle of thevehicle 14.

With further reference to FIG. 5, the output hitch angle of p(κ₂, δ) isprovided as the reference signal, γ_(ref), for the remainder of thecontrol system, although the steering angle δ value used by thecurvature regulator 92 is feedback from the non-linear function of thehitch angle regulator 90. It is shown that the hitch angle regulator 90uses feedback linearization for defining a feedback control law, asfollows:

${g\left( {u,\gamma,v} \right)} = {\delta = {\tan^{- 1}\left( {\frac{W}{v\left( {1 + {\frac{L}{D}{\cos (\gamma)}}} \right)}\left( {{\frac{v}{D}{\sin (\gamma)}} - u} \right)} \right)}}$

As also shown in FIG. 5, the feedback control law, g(u, γ, v), isimplemented with a proportional integral (PI) controller, whereby theintegral portion substantially eliminates steady-state tracking error.More specifically, the control system illustrated in FIG. 58 may beexpressed as the following differential-algebraic equations:

$\mspace{20mu} {{\overset{.}{\gamma}(t)} = {{\frac{v(t)}{D}{\sin \left( {\gamma (t)} \right)}} + {\left( {1 + {\frac{L}{D}{\cos \left( {\gamma (t)} \right)}}} \right)\frac{v(t)}{W}\overset{\_}{\delta}}}}$${\tan (\delta)} = {\overset{\_}{\delta} = {\frac{W}{{v(t)}\left( {1 + {\frac{L}{D}{\cos \left( {\gamma (t)} \right)}}} \right)}\left( {{K_{P}\left( {{p\left( {\kappa_{2},\delta} \right)} - {\gamma (t)}} \right)} - {\frac{v(t)}{D}{\sin \left( {\gamma (t)} \right)}}} \right)}}$

It is contemplated that the PI controller may have gain terms based ontrailer length D since shorter trailers will generally have fasterdynamics. In addition, the hitch angle regulator 90 may be configured toprevent the desired hitch angle γ(d) to reach or exceed a jackknifeangle γ(j), as computed by the controller or otherwise determined by thetrailer backup assist system 10, as disclosed in greater detail herein.

Referring now to FIG. 6, in the illustrated embodiments of the disclosedsubject matter, it is desirable to limit the potential for the vehicle14 and the trailer 12 to attain a jackknife angle (i.e., thevehicle/trailer system achieving a jackknife condition). A jackknifeangle γ(j) refers to a hitch angle γ that while backing cannot beovercome by the maximum steering input for a vehicle such as, forexample, the steered front wheels of the vehicle 14 being moved to amaximum steered angle δ at a maximum rate of steering angle change. Thejackknife angle γ(j) is a function of a maximum wheel angle for thesteered wheels of the vehicle 14, the wheel base W of the vehicle 14,the distance L between hitch point and the rear axle of the vehicle 14,and the length D between the hitch point and the axle of the trailer 12or the effective axle when the trailer 12 has multiple axles. When thehitch angle γ for the vehicle 14 and the trailer 12 achieves or exceedsthe jackknife angle γ(j), the vehicle 14 may be pulled forward to reducethe hitch angle γ.

A kinematic model representation of the vehicle 14 and the trailer 12can also be used to determine a jackknife angle for the vehicle-trailercombination. Accordingly, with reference to FIGS. 3 and 6, a steeringangle limit for the steered front wheels requires that the hitch angle γcannot exceed the jackknife angle γ(j), which is also referred to as acritical hitch angle γ. Thus, under the limitation that the hitch angleγ cannot exceed the jackknife angle γ(j), the jackknife angle γ(j) isthe hitch angle γ that maintains a circular motion for thevehicle/trailer system when the steered wheels 64 are at a maximumsteering angle δ(max). The steering angle for circular motion with hitchangle γ is defined by the following equation.

${\tan \; \delta_{\max}} = \frac{w\; \sin \; \gamma_{\max}}{D + {L\; \cos \; \gamma_{\max}}}$

Solving the above equation for hitch angle γ allows jackknife angle γ(j)to be determined. This solution, which is shown in the followingequation, can be used in implementing trailer backup assistfunctionality in accordance with the disclosed subject matter formonitoring hitch angle γ in relation to jackknife angle.

${\cos \; \overset{\_}{\gamma}} = \frac{{- b} \pm \sqrt{b^{2} - {4\; {ac}}}}{2\; a}$

where,

a=L² tan²δ(max)+W²;

b=2 LD tan²δ(max); and

c=D² tan²δ(max)−W².

In certain instances of backing the trailer 12, a jackknife enablingcondition can arise based on current operating parameters of the vehicle14 in combination with a corresponding hitch angle γ. This condition canbe indicated when one or more specified vehicle operating thresholds aremet while a particular hitch angle γ is present. For example, althoughthe particular hitch angle γ is not currently at the jackknife angle forthe vehicle 14 and attached trailer 12, certain vehicle operatingparameters can lead to a rapid (e.g., uncontrolled) transition of thehitch angle γ to the jackknife angle for a current commanded trailercurvature and/or can reduce an ability to steer the trailer 12 away fromthe jackknife angle. One reason for a jackknife enabling condition isthat trailer curvature control mechanisms (e.g., those in accordancewith the disclosed subject matter) generally calculate steering commandsat an instantaneous point in time during backing of a trailer 12.However, these calculations will typically not account for lag in thesteering control system of the vehicle 14 (e.g., lag in a steering EPAScontroller). Another reason for the jackknife enabling condition is thattrailer curvature control mechanisms generally exhibit reduced steeringsensitivity and/or effectiveness when the vehicle 14 is at relativelyhigh speeds and/or when undergoing relatively high acceleration.

Jackknife determining information may be received by the controller 28,according to one embodiment, to process and characterize a jackknifeenabling condition of the vehicle-trailer combination at a particularpoint in time (e.g., at the point in time when the jackknife determininginformation was sampled). Examples of the jackknife determininginformation include, but are not limited to, information characterizingan estimated hitch angle γ, information characterizing a vehicleaccelerator pedal transient state, information characterizing a speed ofthe vehicle 14, information characterizing longitudinal acceleration ofthe vehicle 14, information characterizing a brake torque being appliedby a brake system of the vehicle 14, information characterizing apowertrain torque being applied to driven wheels of the vehicle 14, andinformation characterizing the magnitude and rate of driver requestedtrailer curvature. In this regard, jackknife determining informationwould be continually monitored, such as by an electronic control unit(ECU) that carries out trailer backup assist (TBA) functionality. Afterreceiving the jackknife determining information, a routine may processthe jackknife determining information for determining if thevehicle-trailer combination attained the jackknife enabling condition atthe particular point in time. The objective of the operation forassessing the jackknife determining information is determining if ajackknife enabling condition has been attained at the point in timedefined by the jackknife determining information. If it is determinedthat a jackknife enabling condition is present at the particular pointin time, a routine may also determine an applicable countermeasure orcountermeasures to implement. Accordingly, in some embodiments, anapplicable countermeasure will be selected dependent upon a parameteridentified as being a key influencer of the jackknife enablingcondition. However, in other embodiments, an applicable countermeasurewill be selected as being most able to readily alleviate the jackknifeenabling condition. In still another embodiment, a predefinedcountermeasure or predefined set of countermeasures may be theapplicable countermeasure(s).

As previously disclosed with reference to the illustrated embodiments,during operation of the trailer backup assist system 10, a driver of thevehicle 14 may be limited in the manner in which steering inputs may bemade with the steering wheel 68 of the vehicle 14 due to the powerassist steering system 62 being directly coupled to the steering wheel68. Accordingly, the steering input device 18 of the trailer backupassist system 10 may be used for inputting a desired curvature 26 of thetrailer 12, thereby decoupling such commands from being made at thesteering wheel 68 of the vehicle 14. However, additional embodiments ofthe trailer backup assist system 10 may have the capability toselectively decouple the steering wheel 68 from movement of steerablewheels of the vehicle 14, thereby allowing the steering wheel 68 to beused for commanding changes in the desired curvature 26 of a trailer 12or otherwise selecting a desired backing path during such trailer backupassist.

Referring now to FIG. 7, one embodiment of the steering input device 18is illustrated disposed on a center console 108 of the vehicle 14proximate a shifter 110. In this embodiment, the steering input device18 includes a rotatable knob 30 for providing the controller 28 with thedesired backing path of the trailer 12. More specifically, the angularposition of the rotatable knob 30 may correlate with a desiredcurvature, such that rotation of the knob to a different angularposition provides a different desired curvature with an incrementalchange based on the amount of rotation and, in some embodiments, anormalized rate, as described in greater detail herein.

The rotatable knob 30, as illustrated in FIGS. 7-8, may be biased (e.g.,by a spring return) to a center or at-rest position P(AR) betweenopposing rotational ranges of motion R(R), R(L). In the illustratedembodiment, a first one of the opposing rotational ranges of motion R(R)is substantially equal to a second one of the opposing rotational rangesof motion R(L), R(R). To provide a tactile indication of an amount ofrotation of the rotatable knob 30, a force that biases the knob towardthe at-rest position P(AR) can increase (e.g., non-linearly) as afunction of the amount of rotation of the rotatable knob 30 with respectto the at-rest position P(AR). Additionally, the rotatable knob 30 canbe configured with position indicating detents such that the driver canpositively feel the at-rest position P(AR) and feel the ends of theopposing rotational ranges of motion R(L), R(R) approaching (e.g., softend stops). The rotatable knob 30 may generate a desired curvature valueas function of an amount of rotation of the rotatable knob 30 withrespect to the at-rest position P(AR) and a direction of movement of therotatable knob 30 with respect to the at-rest position P(AR). It is alsocontemplated that the rate of rotation of the rotatable knob 30 may alsobe used to determine the desired curvature output to the controller 28.The at-rest position P(AR) of the knob corresponds to a signalindicating that the vehicle 14 should be steered such that the trailer12 is backed along a substantially straight backing path (zero trailercurvature request from the driver), as defined by the longitudinaldirection 22 of the trailer 12 when the knob was returned to the at-restposition P(AR). A maximum clockwise and anti-clockwise position of theknob (i.e., limits of the opposing rotational ranges of motion R(R),R(L)) may each correspond to a respective signal indicating a tightestradius of curvature (i.e., most acute trajectory or smallest radius ofcurvature) of a path of travel of the trailer 12 that is possiblewithout the corresponding vehicle steering information causing ajackknife condition.

As shown in FIG. 8, a driver can turn the rotatable knob 30 to provide adesired curvature 26 while the driver of the vehicle 14 backs thetrailer 12. In the illustrated embodiment, the rotatable knob 30 rotatesabout a central axis between a center or middle position 114corresponding to a substantially straight backing path 26 of travel, asdefined by the longitudinal direction 22 of the trailer 12, and variousrotated positions 116, 118, 120, 122 on opposing sides of the middleposition 114, commanding a desired curvature 26 corresponding to aradius of the desired backing path of travel for the trailer 12 at thecommanded rotated position. It is contemplated that the rotatable knob30 may be configured in accordance with embodiments of the disclosedsubject matter and omit a means for being biased to an at-rest positionP(AR) between opposing rotational ranges of motion. Lack of such biasingmay allow a current rotational position of the rotatable knob 30 to bemaintained until the rotational control input device is manually movedto a different position. It is also conceivable that the steering inputdevice 18 may include a non-rotational control device that may beconfigured to selectively provide a desired curvature 26 and to overrideor supplement an existing curvature value. Examples of such anon-rotational control input device include, but are not limited to, aplurality of depressible buttons (e.g., curve left, curve right, andtravel straight), a touch screen on which a driver traces or otherwiseinputs a curvature for path of travel commands, a button that istranslatable along an axis for allowing a driver to input backing pathcommands, or a joystick type input and the like.

Referring to FIG. 9, an example of using the steering input device 18for dictating a curvature of a desired backing path of travel (POT) ofthe trailer 12 while backing up the trailer 12 with the vehicle 14 isshown. In preparation of backing the trailer 12, the driver of thevehicle 14 may drive the vehicle 14 forward along a pull-thru path (PTP)to position the vehicle 14 and trailer 12 at a first backup position Bl.In the first backup position Bl, the vehicle 14 and trailer 12 arelongitudinally aligned with each other such that a longitudinalcenterline axis L1 of the vehicle 14 is aligned with (e.g., parallelwith or coincidental with) a longitudinal centerline axis L2 of thetrailer 12. It is disclosed herein that such alignment of thelongitudinal axis L1, L2 at the onset of an instance of trailer backupfunctionality is not a requirement for operability of a trailer backupassist system 10, but may be done for calibration.

After activating the trailer backup assist system 10 (e.g., before,after, or during the pull-thru sequence), the driver begins to back thetrailer 12 by reversing the vehicle 14 from the first backup positionB1. So long as the rotatable knob 30 of the trailer backup steeringinput device 18 remains in the at-rest position P(AR) and no othersteering input devices 18 are activated, the trailer backup assistsystem 10 will steer the vehicle 14 as necessary for causing the trailer12 to be backed along a substantially straight path of travel, asdefined by the longitudinal direction 22 of the trailer 12, specificallythe centerline axis L2 of the trailer 12, at the time when backing ofthe trailer 12 began. When the trailer 12 reaches the second backupposition B2, the driver rotates the rotatable knob 30 to command thetrailer 12 to be steered to the right (i.e., a knob position R(R)clockwise rotation). Accordingly, the trailer backup assist system 10will steer the vehicle 14 for causing the trailer 12 to be steered tothe right as a function of an amount of rotation of the rotatable knob30 with respect to the at-rest position P(AR), a rate movement of theknob, and/or a direction of movement of the knob with respect to theat-rest position P(AR). Similarly, the trailer 12 can be commanded tosteer to the left by rotating the rotatable knob 30 to the left. Whenthe trailer 12 reaches backup position B3, the driver allows therotatable knob 30 to return to the at-rest position P(AR) therebycausing the trailer backup assist system 10 to steer the vehicle 14 asnecessary for causing the trailer 12 to be backed along a substantiallystraight path of travel as defined by the longitudinal centerline axisL2 of the trailer 12 at the time when the rotatable knob 30 was returnedto the at-rest position P(AR). Thereafter, the trailer backup assistsystem 10 steers the vehicle 14 as necessary for causing the trailer 12to be backed along this substantially straight path to the fourth backupposition B4. In this regard, arcuate portions of a path of travel POT ofthe trailer 12 are dictated by rotation of the rotatable knob 30 andstraight portions of the path of travel POT are dictated by anorientation of the centerline longitudinal axis L2 of the trailer 12when the knob is in/returned to the at-rest position P(AR).

In the embodiment illustrated in FIG. 9, in order to activate thetrailer backup assist system 10, the driver interacts with the trailerbackup assist system 10 and the automatically steers as the driverreverses the vehicle 14. As discussed above, the driver may command thetrailer backing path by using a steering input device 18 and thecontroller 28 may determine the vehicle steering angle to achieve thedesired curvature 26, whereby the driver controls the throttle and brakewhile the trailer backup assist system 10 controls the steering.

With reference to FIG. 10, a method of operating one embodiment of thetrailer backup assist system 10 is illustrated, shown as one embodimentof the operating routine 132 (FIG. 2). At step 134, the method isinitiated by the trailer backup assist system 10 being activated. It iscontemplated that this may be done in a variety of ways, such a making aselection on the display 82 of the vehicle HMI 80. The next step 136,then determines the kinematic relationship between the attached trailer12 and the vehicle 14. To determine the kinematic relationship, variousparameters of the vehicle 14 and the trailer 12 must be sensed, input bythe driver, or otherwise determined for the trailer backup assist system10 to generate steering commands to the power assist steering system 62in accordance with the desired curvature or backing path 26 of thetrailer 12. As disclosed with reference to FIGS. 3-6, the kinematicparameters to define the kinematic relationship include a length of thetrailer 12, a wheel base of the vehicle 14, a distance from a hitchconnection to a rear axle of the vehicle 14, and a hitch angle γ betweenthe vehicle 14 and the trailer 12, among other variables and parametersas previously described. Accordingly, after the kinematic relationshipis determined, the trailer backup assist system 10 may proceed at step160 to determine the current hitch angle by processing the hitch angleestimation routine 130.

As shown in FIG. 11, one embodiment of the trailer sensor module 20 isillustrated having a housing 21 removably attached to the trailer 12,although the housing may be welded or otherwise permanently fixed to thetrailer 12 in additional embodiments of the sensor module 20. Thehousing 21 of the illustrated embodiment is shaped as a rectangularprism with a bottom surface 19 in abutting contact with an upper surface35 of the tongue 36 of the trailer 12. Various shapes and designs of thehousing 21 are contemplated for additional embodiments to account fordifferently packaged components, specific weather or environmentalconditions, and aesthetic purposes, among other considerations. Toprevent the housing 21 from moving relative to the tongue 36, a surfacefeature may be provided integrally or separately on at least one of thebottom surface 19 of the housing 21 and the upper surface 35 of thetongue 36, such as an elastomeric pad, an adhesive, or an etching forincreasing friction therebetween. Also to provide secure attachment, theillustrated embodiment includes a strap 33 that connects betweenopposing lateral sides of the housing 21 and surrounds the tongue 36.The strap 33 may be made from any conventional material, such as nylon,leather, or rubber, and is configured to be tightened to secure againstat least a lower surface 37 of the tongue 36. Various means oftightening the strap 33 may be implemented, as generally understood inthe art.

As also depicted in the embodiment illustrated in FIGS. 11-12, a topsurface 15 of the housing 21 is defined by an exposure surface of asolar element 39 coupled with the housing 21 for providing electricityto the sensor module 20. The illustrated sensor module 20 also includesa battery 41 electrically connected to the solar element 39 for storingelectricity generated by the solar element 39 and supplying electricityto the components of the sensor module 20. The solar element 39 may be apanel or any other form or configuration of photovoltaic cells orportions thereof having material for converting solar energy toelectricity. In additional embodiments of the sensor module 20, thesolar element 39 may be omitted or otherwise configured, which may allowthe top surface 15 of the housing 21, in some embodiments, to includethe target 52 (FIG. 1) for the vision-based hitch angle sensor 44.

With further reference to FIG. 12, the illustrated housing 21 is shownenclosing the wireless transmitter 29, the yaw rate sensor 25, and theaccelerometer 27. It is contemplated that the housing 21 may enclose allor a portion of the components of the sensor module 20. The housing 21may also be hermetically sealed or otherwise sealed with a fluid seal toprevent the enclosed components from being exposed to liquid, dust, orother debris that may damage or cause the sensor module 20 tomalfunction. In one embodiment, the fluid seal may include a gasketsecured along a seam of the housing to provide the protective fluidsealing.

The sensor module shown in FIG. 12 is shown with the wirelesstransmitter 29 in communicable range from the wireless receiver 31 ofthe vehicle 14, depicted attached to the tongue 36 of the trailer 12 atin an acceptable distance 170, less than a proximity distance 172. Thewireless receiver 31 is configured to communicate with and receivesignals within the proximity distance 172, defined as a distance from arear portion 174 of the vehicle 14, beyond which communication with thewireless receiver 31 is not likely to be associated with a trailerattached to the vehicle 14. The controller 28 may estimate the distanceat which the wireless transmitter 29 is located away from the receiver31 based on the strength of the transmitted signals from the wirelesstransmitter 29. Accordingly, the illustrated wireless transmitter 29 isattached to the trailer 12 within the proximity distance 172 to be incommunicable range with the wireless receiver 31. It is contemplatedthat the wireless receiver 31 may also be used for receiving signalsemitted from a key fob, such as door lock and unlock commands, hatchopen commands, vehicle ignition start commands, and other conceivablecommands.

In one embodiment, the wireless transmitter 29 may consistently emit aradio frequency transmission, such that the vehicle 14 determines thatthe trailer 12 associated with the radio frequency transmission has beendetached from the hitch ball 40 or hitch of the vehicle 14 when thewireless receiver 31 of the vehicle 14 fails to receive the radiofrequency transmission for a threshold period of time, such as 3 secondsor another conceivable time period during which the radio frequencytransmission was expected to be received. Also, the vehicle 14 maydetermine that the trailer 12 associated with the radio frequencytransmission has been detached from the hitch ball 40 or hitch of thevehicle 14 when signal strength of the transmissions from the wirelesstransmitter 29 are indicative of the wireless transmitter movingrearward a distance beyond the length of the trailer or otherwiseoutside of the proximity distance 172. In an instance when thecontroller 28 of the vehicle 14 determines that the trailer 12 may bedetached, a warning may be generated to the driver via the vehicle HMI80 and/or the vehicle alert system 76.

Referring now to FIG. 13, an embodiment of the sensor module 20 isschematically illustrated to show a sensor module controller 43 that maybe used to control the transmission of radio signals and the operationof the sensors of the sensor module 20. The sensors illustrated includea yaw rate sensor 25 that generates a yaw rate of the trailer 12 for usein determining the hitch angle γ. The sensors of the illustratedembodiment of the sensor module 20 also include an accelerometer 27 forsensing the lateral acceleration of the trailer 12 for use indetermining the trailer position and movement. It is contemplated thatthe sensor module 20 may include additional or alternative sensors fromthose illustrated for determining a dynamic parameter of the trailer 12or a constant parameter of the trailer 12. For instance, in oneembodiment the sensor module 20 may include a positional sensor thatdetermines the location of the target 52 on the trailer tongue 36 forthe vision-based hitch angle sensor 44. Another conceivable sensor ofthe sensor module 20 for determining a constant parameter of the trailer12 includes a height sensor to determine the distance of the tongue 36away from the ground surface, which may be used to assist with thevision-based hitch angle sensor 44 or take into consideration the pitchof the trailer 12 in operating the trailer backup assist system 10.

As also shown in FIG. 13, the sensor module controller 43 includes amicroprocessor 45 to process logic and routines stored in acorresponding memory unit 47 of the sensor module controller 43. Assuch, the memory unit 47 may store a unique identifier for the wirelesstransmitter 29 to emit, such as a radio frequency with a coded signalconfigured for the controller 28 on the vehicle to decode and associatewith the sensor module 20 and any corresponding trailer. In theillustrated embodiment, the sensor module controller 43 may communicatewith the wireless receiver 31 of the trailer backup assist system 10 viathe wireless transmitter 29 to determine when the unique identifier hasbeen received and decoded, so it may proceed to transmit a parameter ofthe trailer 12, as described in more detail below. The sensor modulecontroller 43, in additional embodiments, may be a stand-alone dedicatedcontroller or may be a shared controller integrated with other controlfunctions, such as integrated with the controller 28 of the trailerbackup assist system 10, the power assist steering system 62, and otherconceivable onboard or off-board vehicle control systems. Accordingly,it is contemplated that in one embodiment, the sensor module 20 maytransmit both the unique identifier and the parameter simultaneouslywithout a sensor module controller 43, such that the controller 28 onthe vehicle 14 may accesses the parameter after the unique identifier isrecognized to be from a sensor module 20 on a trailer 12 attached to thevehicle.

One embodiment of a method of identifying a trailer 12 having a sensormodule 20 is shown in FIG. 14, where at step 176 the unique identifieris transmitted with the wireless transmitter 29 of the sensor module 20.At step 178, the wireless receiver 31 on the vehicle 14 receives theunique identifier and performs an operation to determine if the uniqueidentifier is associated with a known trailer or a trailer otherwisedetermined to be compatible with the vehicle 14. This operation mayinclude decoding a coded signal of the unique identifier to determine ifthe unique identifier is recognizable or otherwise contained within adatabase of the memory 86 before accessing the parameter of the trailer12. At step 180, the vehicle 14 may access a parameter of the trailer 12based on the recognized unique identifier. In one embodiment, theparameter is a dimension of the trailer 12 saved in the memory unit 47of the sensor module controller 43 or the controller 28 of the trailerbackup assist system 10, such as a length of the trailer 12 or othernecessary variable of the kinematic relationship used to generatesteering commands for the vehicle 14 to guide the trailer along thedesired backing path 26. In another embodiment, the parameter may be adynamic variable of the trailer 12, such as a yaw rate ω₂ of the trailer12 sensed by the yaw rate sensor 25 of the sensor module 20. It is alsocontemplated that the parameter may include multiple variables, bothdynamic and static variable that provide the trailer backup assistsystem 10 with more accurate steering commands to guide the trailer 12along the desired backing path 26. Further, at step 182, it iscontemplated that in one embodiment, the controller 28 may monitor thewireless transmissions to determine that the trailer associated withunique identifier is coupled with the vehicle based on, at step 184determining that the wireless receiver 31 consistently receives thecontinuous or otherwise intermittent signals from the wirelesstransmitter 29. At step 186, it is conceivable that it may be determinedthat the trailer 12 associated with unique identifier is no longerattached to the vehicle 14 due to a failure to receive the radiofrequency transmission from the transmitter 29 for a threshold period oftime.

Referring again to FIG. 3, one embodiment of a kinematic relationshipbetween the trailer 12 and the vehicle 14 is developed with theillustrated schematic diagram that shows the geometry of a vehicle and atrailer overlaid with a two-dimensional x-y coordinate system,identifying variables, such as the trailer yaw rate ω₂ and the vehicleyaw rate ω₁, which are used to determine the corresponding hitch angleγ. As such, hitch angle estimation may be determined using trailer yawrate signal ω₂, vehicle speed signal v₁ and vehicle yaw rate signal ω₁.More specifically, the yaw rate of the trailer may be given by thefollowing kinematic equation, which can also be rearranged to estimatetrailer hitch angle γ:

$\omega_{2} = {{\frac{v_{1}}{D}\sin \; \gamma} - {\frac{L}{D}\cos \; {\gamma\omega}_{1}}}$

Referring now to FIG. 15, one embodiment of the hitch angle estimationroutine 130 is illustrated, whereby the above-noted kinematicrelationship is utilized to instantaneously estimate the hitch angle γ.This routine may be used in conjunction with operation of the trailersensor module to provide the instantaneously estimate the hitch angle γ.At step 138, the sensor signals are received for executing the steps todetermine the hitch angle γ. The sensor signals may include the traileryaw rate signal ω₂, the vehicle speed signal v₁, and the vehicle yawrate signal ω₁, along with other sensor signals that may be used in someembodiments, such as the steering angle δ signal, trailer lateralacceleration a_(y2), the measure hitch angle from the hitch angle sensor44 among other potential sensor signals. At step 140, these signals maybe filtered and any potential offsets may be compensated beforeproceeding to further process the sensor signals.

Still referring to FIG. 15, in one embodiment, the vehicle speed v₁ maybe received from the speed sensor 58 on the vehicle 14 and not requireany further processing or derivation to proceed with calculating theinstantaneous hitch angle γ. However, at step 142, in some embodiments,the vehicle speed v₁ may be derived from wheel speed sensors on thevehicle 14, the positioning device 56, or other conceivable means todetermine the vehicle speed v₁. Also, according to one embodiment, thevehicle yaw rate ω₁ may be received directly from the yaw rate sensor 60on the vehicle 14 and not necessitate any further derivation. However,it is also contemplated that at step 142, the vehicle yaw rate ω₁ mayadditionally or alternatively be derived from left and right wheel speedsensors on the vehicle14. Further, according to an additionalembodiment, the vehicle yaw rate ω₁ may be derived from the steeringangle δ of the vehicle 14 and the vehicle speed v₁, along with thevehicle wheelbase W, which is known or otherwise stored in the memory 86of the controller 28. In one embodiment, the vehicle yaw rate ω₁ may bedetermined based on the steering angle δ, the vehicle wheelbase W, andthe vehicle speed v₁.

As shown in FIG. 15, the trailer yaw rate ω₂ may also be provideddirectly by the sensor system 16 at step 138 or determined fromprocessing the sensor signals at step 142. For instance, the trailer yawrate ω₂ may be received directly from the yaw rate sensor 25 of thesensor module 20 mounted on the trailer 12. Additionally oralternatively, the trailer yaw rate ω₂ may be derived from the left andright wheel speed sensors 23 on the trailer 12. Also, in addition or inthe alternative, the trailer yaw rate ω₂ may be calculated using thetrailer speed v₂ and the lateral acceleration a_(y2) of the trailer, assensed by the accelerometer 27 of the trailer sensor module 20, in oneembodiment. One embodiment to determine the trailer yaw rate ω₂ islateral acceleration a_(y2) of the trailer divided by the trailer speedv₂, where lateral acceleration a_(y2) of the trailer may be derived fromthe accelerometer 27 and trailer speed v₂ may be derived from the wheelspeed sensor.

When wheel speed sensors 23 are not available or otherwise included onthe trailer sensor module 20 or the sensor system 16, theabove-referenced kinematic equation may then be reordered to solve forthe trailer speed v₂. As such, the accuracy of the trailer speed v₂ andthe resultant calculated hitch angle γ will rely more heavily on theaccuracy of the other sensors utilized to determine the vehicle speedv₁, vehicle yaw rate ω₁, and the trailer yaw rate ω₂, as previouslymentioned, along with the accuracy of the vehicle and trailer dimensionsL and D.

As illustrated in FIG. 15, when the sensor signals have been receivedand the necessary parameters received or otherwise determined, at step144, the controller 28 processes the following equation, based on thekinematic relationship of the trailer 12 and the vehicle 14, to solvefor the instantaneous hitch angle γ.

$\gamma = {\sin^{- 1}\left( \frac{{v_{1}\omega_{2}D} + {\omega_{1}L\sqrt{v_{1}^{2} + {\omega_{1}^{2}L^{2}} - {\omega_{2}^{2}D^{2}}}}}{v_{1}^{2} + {\omega_{1}^{2}L^{2}}} \right)}$

Further, should the sensor system 16 be unequipped to provide thecontroller 28 with the trailer yaw rate ω₂, in another embodiment, atstep 144, the instantaneous hitch angle γ may still be determined, asfollows:

$\gamma = {\sin^{- 1}\frac{{v_{2}\omega_{1}L} \pm {v_{1}\sqrt{v_{1}^{2} + {\omega_{1}^{2}L^{2}} - v_{2}^{2}}}}{v_{1}^{2} + {\omega_{1}^{2}L^{2}}}\mspace{14mu} {or}}$$\gamma = {{\sin^{- 1}\frac{v_{2}}{\sqrt{v_{1}^{2} + {\omega_{1}^{2}L^{2}}}}} - {\tan^{- 1}{\frac{v_{1}}{\omega_{1}L}.}}}$

In this equation, the hitch angle γ is determined based on the vehiclespeed v₁, trailer speed v₂, and vehicle yaw rate ω₁, whereby suchparameters are relied upon more heavily for accuracy. The above equationsolving for the hitch angle γ is based on a kinematic relationship forthe trailer speed v₂, which does not incorporate the trailer yaw rateω₂. With this identified relationship, it is conceivable that if thehitch angle is known by another means, such the hitch angle sensor 44,and the trailer speed v₂ may therefore be solved for with the aboveequation. Also, trailer speed v₂ may be determined based on the traileryaw rate ω₂ and the lateral acceleration a_(y2) of the trailer, such asfrom the trailer yaw rate sensor 25 and the accelerometer 27,respectively. Accordingly, when the trailer speed v₂ is sensed orotherwise determined from other variables, such as the trailer yaw rateω₂ and the lateral acceleration a_(y2) of the trailer, then the hitchangle γ calculation may incorporate this parameter to provide a moreaccurate value.

Referring again to FIG. 15, at step 146 the presently estimated hitchangle γ may be filtered to provide a more accurate estimate. Morespecifically, the hitch angle γ estimated with the hitch angleestimation routine 130 may be less accurate at low vehicle speed v₁ whenthe denominator of the above-noted equations approaches zero. In oneembodiment, the hitch angle γ may be filtered by using the trailer yawrate ω₂ and the vehicle yaw rate ω₁. For instance, the estimated hitchangle γ could be filtered with a discrete-time Kalman filter, wherebythe filtered estimate is obtained from the following equation:

{circumflex over (γ)}_(k−1)={circumflex over (γ)}_(k)+(ω_(2,k)−ω_(1,k)0·T _(s) +K _(k)·(γ_(k)−{circumflex over (γ)}_(k)).

In this embodiment, T_(s) is the sampling time, k is an integerrepresenting the k^(th) sampling instance, K_(k) is the Kalman gain, andγ_(k) is the calculated hitch angle from the above-noted equations.However, when the vehicle 14 is stopped, the filtered estimate is“frozen” at the previously known good value (e.g. {circumflex over(γ)}_(k+1)={circumflex over (γ)}_(k)). This is the filter to determinewhen the vehicle 14 is stopped or traveling at low speeds, as providedat step 148, which precedes step 144. If the vehicle 14 is notdetermined to be stopped or traveling slow at step 148, the hitch angleγ is estimated and filtered at steps 144 and 146, as described above.When the result of an accurate hitch angle γ from the above-notedkinematic equations is temporarily not available or inaccurate (e.g., atlow speed), the filtered estimate is obtained from the followingequation:

{circumflex over (γ)}_(k−1)={circumflex over(γ)}_(k)+(ω_(2,k)−ω_(1,k))·T _(s).

In an additional or alternative embodiment, the hitch angle γ may befiltered by using the vehicle yaw rate ω₁ and vehicle speed v₁. Forinstance, this may be desired if the trailer yaw rate ω₂ is noisy,whereby the filtering described above and shown in FIG. 15 may notgenerate desired results. In this case, a nonlinear extension of theKalman filter may be applied, which is often referred to as an extendedKalman filter by those skilled in the art. To do so, when the resultsare generally available and accurate for the hitch angle γ determined atstep 144, such as when the vehicle 14 is moving a sufficient speed, thefilter may be estimated from the following equation:

${\hat{\gamma}}_{k + 1} = {{\hat{\gamma}}_{k} + {\left( {{\frac{v_{1,k}}{D}\sin \; {\hat{\gamma}}_{k}} - {\frac{\omega_{1,k} \cdot L}{D}\cos \; {\hat{\gamma}}_{k}} - \omega_{1,k}} \right) \cdot T_{s}} + {K_{k} \cdot \left( {\gamma_{k} - {\hat{\gamma}}_{k}} \right)}}$

Accordingly, when the results are temporarily not available orinaccurate for the hitch angle γ determined at step 144, such as at lowspeeds, the filtered estimate may is obtained from the followingequation:

${\hat{\gamma}}_{k + 1} = {{\hat{\gamma}}_{k} + {\left( {{\frac{v_{1,k}}{D}\sin \; {\hat{\gamma}}_{k}} - {\frac{\omega_{1,k} \cdot L}{D}\cos \; {\hat{\gamma}}_{k}} - \omega_{1,k}} \right) \cdot T_{s}}}$

There are many alternative ways to express the Kalman gain, and one ofthe formulations is given as follows:

${A_{k} = {{\left( {{\frac{v_{1,k}}{D}\cos \; {\hat{\gamma}}_{k}} + {\frac{\omega_{1,k} \cdot L}{D}\sin \; {\hat{\gamma}}_{k}}} \right) \cdot T_{s}} + 1}},{K_{k} = {P_{k}\left( {P_{k} + R} \right)}^{- 1}},{P_{k + 1} = {{{A_{k}\left( {1 - K_{k}} \right)}P_{k}A_{k}^{T}} + Q}},$

where A_(k) is the derivative matrix, Q is the process noise covariance,R is the measurement noise covariance, and P_(k) is the estimation errorcovariance.

As shown in FIG. 15, upon estimating and filtering the hitch angle γ, atstep 152 the trailer length D and vehicle wheelbase W can be estimatedor refined to improve the accuracy of later calculations. As such,trailer length D may be estimated based on the trailer speed v₂, thevehicle speed v₁, the vehicle yaw rate ω₁, and the trailer yaw rate ω₂,as determined from the previous steps of the hitch angle estimationroutine 130. For instance, if the length L between hitch point and rearaxle of the vehicle 14 is measured or otherwise known, the trailerlength D can be calculated as follows:

$D = {\sqrt{\frac{v_{1}^{2} + {\omega_{1}^{2}L^{2}} - v_{2}^{2}}{\omega_{2}^{2}}}.}$

Similarly, if the trailer length D is measured or otherwise known, thelength L between hitch point and rear axle of the vehicle 14 may beestimated based on the trailer speed v₂, the vehicle speed v₁, thevehicle yaw rate ω₁, and the trailer yaw rate ω₂, as determined from theprevious steps of the hitch angle estimation routine 130. As such, thelength L can be calculated as follows:

$L = {\sqrt{\frac{v_{2}^{2} + {\omega_{2}^{2}D^{2}} - v_{1}^{2}}{\omega_{1}^{2}}}.}$

As also shown in FIG. 15, at step 154 the hitch angle estimation routine130 may proceed to estimate or refine the trailer turning radius r₂ andthe curvature κ₂ of the trailer trajectory for improving the accuracy oflater calculations. This may be done using the following equations:

${r_{2} = \frac{v_{2}}{\omega_{2}}},{and}$$\kappa_{2} = {\frac{\omega_{2}}{v_{2}}.}$

Referring again to FIG. 10, at step 160 the hitch angle γ is determinedbetween the vehicle 14 and the trailer 12, although this may be donecontinuously during operation of the trailer backup assist system 10. Itis contemplated that in additional embodiments of the trailer backupassist system 10 that the steps of determining the kinematicrelationship and sensing the hitch angle γ may occur before the trailerbackup assist system 10 is activated or at any other time beforesteering commands are generated. Accordingly, at step 162, the positionand rate of changes is received from the steering input device 18, suchas the angular position and rate of rotation of the rotatable knob 30,for determining the desired curvature 26. At step 164, steering commandsmay be generated based on the desired curvature, correlating with theposition and rate of change of the steering input device 18. Thesteering commands and actuation commands generated may be generated inconjunction with processing of the curvature routine 98, as previousdiscussed. At step 166, the steering commands and actuation commandshave been executed to guide the trailer 12 on the desired curvatureprovided by the steering input device 18.

In parallel with performing the operations for receiving the trailerbackup assist requests, determining the desired curvature 26 of thetrailer 12, and generating the vehicle steering commands, the trailerbackup assist system 10 may perform an operation for monitoring if anunacceptable trailer backup condition exists. Examples of suchmonitoring include, but are not limited to assessing a hitch angle γ todetermine if a hitch angle γ threshold is exceeded, assessing a backupspeed to determine if a backup speed threshold is exceeded, assessingvehicle steering angle to determine if a vehicle steering anglethreshold is exceeded, assessing other operating parameters (e.g.,vehicle longitudinal acceleration, throttle pedal demand rate and hitchangle rate) for determining if a respective threshold value is exceeded,and the like. Backup speed can be determined from the wheel speedinformation obtained from one or more wheel speed sensors 58 of thevehicle 14. If it is determined that an unacceptable trailer backupcondition exists, an operation may be performed for causing the currentpath of travel of the trailer 12 to be inhibited (e.g., stopping motionof the vehicle 14), followed by the operation being performed for endingthe current trailer backup assist instance. It is disclosed herein thatprior to and/or in conjunction with causing the current trailer path tobe inhibited, one or more actions (e.g., operations) can be implementedfor providing the driver with feedback (e.g., a warning) that such anunacceptable hitch angle condition is impending or approaching. In oneexample, if such feedback results in the unacceptable hitch anglecondition being remedied prior to achieving a critical condition, themethod can continue with providing trailer backup assist functionalityin accordance with operations. Otherwise, the method can proceed tooperation for ending the current trailer backup assist instance. Inconjunction with performing the operation for ending the current trailerbackup assist instance, an operation can be performed for controllingmovement of the vehicle 14 to correct or limit a jackknife condition(e.g., steering the vehicle 14, decelerating the vehicle 14, limitingmagnitude and/or rate of driver requested trailer curvature input,limiting magnitude and/or rate of the steering command, and/or the liketo preclude the hitch angle from being exceeded).

With the sensor system 16 and/or controller 28 providing the trailer yawrate ω₂, this parameter may additionally or alternatively be utilized toimprove the electronic stability control provided with the power assiststeering system 62 when the vehicle 14 is towing a trailer. Someelectronic stability control systems use a so called bicycle model(without trailer) to obtain a reference vehicle yaw rate commanded bythe driver. However, when the vehicle is towing a trailer, the towingvehicle may exhibit more oversteer or more understeer tendencies duringa turn, compared to the same vehicle without a trailer attached. Thusthe electronic stability control performance may degrade, and/orunintended activations may occur, when the vehicle is towing a trailer.

By using the sensed or otherwise determined trailer yaw rate signal ω₂,together with other electronic stability control signals, the additionaloversteer or understeer tendencies of the vehicle (compared to when nottowing a trailer) can be identified. Accordingly, the existingelectronic stability control system can be sensitized or desensitized(e.g., by modifying the control thresholds for the brake and enginecontrollers). The brake and engine control actions can also be increasedor reduced by changing the controller gains. Therefore, an additionalcontroller which uses trailer yaw rate signal ω₂ (or the differencebetween trailer and vehicle yaw /rate, i.e., ω₂−ω₁) and its derivativemay be integrated with the existing electronic stability control system.Such a controller is beneficial for improving the overallvehicle-trailer combination stability

In addition, it is contemplated that using the trailer yaw rate signalω₂ and trailer lateral acceleration signal a_(y2), together with otherstandard electronic stability control signals, may further identifyadditional oversteer or understeer tendencies of the vehicle. It is alsoconceivable that a controller that uses the trailer hitch angle γ as afeedback signal may be integrated with the existing electronic stabilitycontrol system for improving the overall vehicle-trailer combinationstability.

As previously mentioned, the hitch angle γ determined by the hitch angleestimation routine 130 may also be used to identify and stabilize aswaying trailer. More specifically, the vehicle-trailer combinationbecomes less damped when its speed is increased. With any driver inputsor external disturbances, the trailer may start to oscillate and theoscillation may sustain for a long time. If the speed is above certain“critical speed”, the system may become unstable, causing theoscillation amplitude to grow larger and eventually cause vehicleinstability and/or a jackknife condition. A controller which usestrailer yaw rate signal ω₂ (or the difference between trailer andvehicle yaw rate, i.e., ω₂−ω₁) and its derivative can be designed toactively control the vehicle/trailer to damping out the oscillation. Inaddition, the trailer yaw rate ω₂ and the trailer lateral accelerationa_(y2), together with other standard electronic stability controlsignals, may be used to stabilize a swaying trailer. Since both traileryaw rate signal ω₂ and trailer lateral acceleration signal a_(y2)directly provide information about the trailer motion, they can be usedto quickly identify whether the trailer is swaying.

It will be understood by one having ordinary skill in the art thatconstruction of the described invention and other components is notlimited to any specific material. Other exemplary embodiments of theinvention disclosed herein may be formed from a wide variety ofmaterials, unless described otherwise herein.

For purposes of this disclosure, the term “coupled” (in all of itsforms, couple, coupling, coupled, etc.) generally means the joining oftwo components (electrical or mechanical) directly or indirectly to oneanother. Such joining may be stationary in nature or movable in nature.Such joining may be achieved with the two components (electrical ormechanical) and any additional intermediate members being integrallyformed as a single unitary body with one another or with the twocomponents. Such joining may be permanent in nature or may be removableor releasable in nature unless otherwise stated.

It is also important to note that the construction and arrangement ofthe elements of the invention as shown in the exemplary embodiments isillustrative only. Although only a few embodiments of the presentinnovations have been described in detail in this disclosure, thoseskilled in the art who review this disclosure will readily appreciatethat many modifications are possible (e.g., variations in sizes,dimensions, structures, shapes and proportions of the various elements,values of parameters, mounting arrangements, use of materials, colors,orientations, etc.) without materially departing from the novelteachings and advantages of the subject matter recited. For example,elements shown as integrally formed may be constructed of multiple partsor elements shown as multiple parts may be integrally formed, theoperation of the interfaces may be reversed or otherwise varied, thelength or width of the structures and/or members or connector or otherelements of the system may be varied, the nature or number of adjustmentpositions provided between the elements may be varied. It should benoted that the elements and/or assemblies of the system may beconstructed from any of a wide variety of materials that providesufficient strength or durability, in any of a wide variety of colors,textures, and combinations. Accordingly, all such modifications areintended to be included within the scope of the present innovations.Other substitutions, modifications, changes, and omissions may be madein the design, operating conditions, and arrangement of the desired andother exemplary embodiments without departing from the spirit of thepresent innovations.

It will be understood that any described processes or steps withindescribed processes may be combined with other disclosed processes orsteps to form structures within the scope of the present invention. Theexemplary structures and processes disclosed herein are for illustrativepurposes and are not to be construed as limiting.

It is also to be understood that variations and modifications can bemade on the aforementioned structures and methods without departing fromthe concepts of the present invention, and further it is to beunderstood that such concepts are intended to be covered by thefollowing claims unless these claims by their language expressly stateotherwise.

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 21. A method of identifying a trailer with a vehicle,comprising: transmitting a unique identifier with a wireless transmitterattached to the trailer; receiving the unique identifier with a wirelessreceiver on the vehicle; determining that the trailer associated withthe unique identifier is coupled with a hitch of the vehicle based onthe wireless receiver consistently receiving signals from the wirelesstransmitter; and accessing a parameter of the trailer based on thereceived unique identifier for autonomously guiding the trailer along adesired backing path.
 22. The method of claim 21, wherein the parameteris a dimension of the trailer saved in a memory unit accessible by acontroller, and wherein the controller recognizes the unique identifierfrom a database before accessing the parameter of the trailer.
 23. Themethod of claim 21, wherein the parameter is a variable of a kinematicrelationship used to generate steering commands for the vehicle to guidethe trailer along the desired backing path.
 24. The method of claim 21,wherein the parameter is a sensed yaw rate of the trailer generated by ayaw rate sensor attached to the trailer.
 25. The method of claim 21,wherein the unique identifier includes a radio frequency with a codedsignal configured for a controller to decode and associate with thetrailer.
 26. The method of claim 21, wherein the wireless receiver isconfigured to receive the unique identifier within a proximity distancefrom a rear portion of the vehicle.
 27. A trailer sensor module forcommunicating with a vehicle, comprising: a yaw rate sensor sensing ayaw rate of a trailer; and a wireless transmitter emitting a uniqueidentifier configured to be recognized by the vehicle and, uponrecognition, transmitting the yaw rate of the trailer to the vehicle.28. The trailer sensor module of claim 27, wherein the yaw rate is usedby the vehicle to determine a hitch angle between the trailer and thevehicle for autonomously guiding the trailer with the vehicle along adesired backing path.
 29. The trailer sensor module of claim 27, furthercomprising a housing enclosing the wireless transmitter and the yaw ratesensor and adapted to be removably attached to the trailer.
 30. Thetrailer sensor module of claim 29, wherein the housing includes a fluidseal to prevent the wireless transmitter and the yaw rate sensor frombeing exposed to liquid.
 31. The trailer sensor module of claim 29,further comprising: a solar element coupled with the housing forproviding electricity to the yaw rate sensor and the wirelesstransmitter.
 32. The trailer sensor module of claim 27, wherein theunique identifier includes a radio frequency with a coded signal emittedto be received by the vehicle within a proximity distance from a rearportion of the vehicle.
 33. The trailer sensor module of claim 27,wherein the wireless transmitter consistently emits a radio frequencytransmission, and wherein the vehicle determines that the trailerassociated with the unique identifier is detached from a hitch of thevehicle when the vehicle fails to receive the radio frequencytransmission for a threshold period of time.
 34. A trailer backup assistsystem for a vehicle reversing a trailer, comprising: a wirelesstransmitter coupled with the trailer and emitting a unique identifier; awireless receiver coupled with the vehicle for receiving the uniqueidentifier; and a controller on the vehicle identifying the trailerbased on the unique identifier and accessing a parameter of theidentified trailer for autonomously guiding the trailer with the vehiclealong a desired backing path, wherein the parameter includes a yaw rateof the trailer generated by a yaw rate sensor attached to the trailer,and wherein upon identification of the trailer, the wireless transmitteremits the yaw rate of the trailer for determining a hitch angle betweenthe vehicle and the trailer.
 35. The trailer backup assist system ofclaim 34, wherein the wireless transmitter is removably coupled with thetrailer.
 36. The trailer backup assist system of claim 34, furthercomprising: a protective housing enclosing the wireless transmitter andadapted to be removably attached to the trailer.
 37. The trailer backupassist system of claim 36, wherein the protective housing includes afluid seal to prevent the wireless transmitter from being exposed toliquid and a solar element for providing electricity to the wirelesstransmitter.
 38. The trailer backup assist system of claim 34, whereinthe parameter includes a dimension of the trailer saved in a memory unitof the controller.
 39. The trailer backup assist system of claim 34,wherein the wireless transmitter consistently emits a radio frequencytransmission, and wherein the controller determines that the trailerassociated with the unique identifier is detached from a hitch of thevehicle when the wireless receiver fails to receive the radio frequencytransmission for a threshold period of time.